Front Range Sub. (CO) - molten sulfur tanker train

[BlockLine_4111]

I have been seeing this molten sulfur tanker train quite regularly rumbling through Longmont, Niwot, Boulder, Louisville and Broomfield. Always Denver bound with 2 locos on the front and the widecab pusher shoving hard, puffing on the rear. Last two times I saw it there was foreign power cut in behind the lead loco. One train last week had a ex-SP leasing company unit in the consist and this weekend's train had UP (aka competitor) power in the lashup.

Questions: where does this train originate and terminate? Symbols? What is molten sulfur used for? Plastics, rubber processing?

Thanks

[BlockLine_4111]

Spotted this train coming down through Niwot at 1:15pm today with BNSF widecab leading, ATSF loco behind and a BNSF widecab pusher on the end.
Surprised to see a pusher on today's short consist. He had plenty of HP, IMO.